I'm a big fan of clipless on my mountain bike. I would be scared not to have it, for my feet sliding off, etc. It helps a lot on uphills, like you said, and makes my feet feel secure on downhills. I would say, just practice more. I really don't have situations anymore where I fall because of my cleats. For general XC and trail riding, I say keep with it. Your confidence will grow and you'll fall less and less. How long have you been using clipless?

For the loose downhills, I find just going down them without hitting the brakes too much is the best option. Of course, unless there is a swtichback at the bottom, then you need the brakes! It's sort of like sand, just float through it, don't touch the brakes, and for flat surfaces, shift down and spin.